There was no immediate comment from the Russian authorities on the Ukrainian accusation.

The Ukrainian presidential administration said the situation was "under control", and there was "no threat to the work of the website".

Several hours after the administration's statement the website was working normally, with all links on the main page being accessible.

Ukraine's decision earlier on Tuesday to impose the ban on Russian sites is a significant ramping up of sanctions on Russia for its annexation of Crimea in 2014 and alleged involvement in the continuing conflict in eastern Ukraine.

Those targeted include social networks VK.com and Odnoklassniki, search engine Yandex and the Mail.ru email service.

Ukrainian service providers have been ordered to block access to the sites.

The companies' offices in Ukraine will also face asset freezes and other restrictions although it was not immediately clear how the ban on the services would come into force and whether Ukraine had the technical means to enforce it.

'Authoritarian state'

The president's decision to push through a decision by Ukraine's national security council could prove controversial domestically, as VK (VKontakte) alone has up to 14 million users in Ukraine and Odnoklassniki (which translates as Classmates) is also widely popular.

How banned social media compare in Ukraine

Image copyrightAFPImage caption
VKontakte alone is thought to have some 15 million users in Ukraine